Solution :
Using standard normal table,
P(Z > z) = 0.10
1 - P(Z < z) = 0.10
P(Z < z) = 1 - 0.10
P(Z < 1.28) = 0.9
z = 1.28
Using z-score formula,
x = z *
+
x = 1.28 * 5 + 28 = 34.4
The capacity of the resevoir is 34.4
option (a)
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